What is the Heat (menstrual) cycle of a female dog?

Our question this week was:

Dr. Debra, we have a 22-month-old female German shepherd. She will be two years old in June can you give me info on their menses, heat cycle (how often they go into heat, etc?). She was in heat for the first time in august 2007.


Susan Aulisio


Hi – thanks for your email asking about the menstruation cycle of dogs. Most dogs generally can go into their first heat somewhere between the ages of 4 months and 18 months. Most dogs are at least 6 months of age and the average is probably between 9 months and 13 months.

Most dogs go into heat twice a year.

Initially, the vulvar lips swell and become soft and pliable. This is the initial stages of heat and can be associated with small amounts of bloody vaginal discharge (many people refer to as the dogs mences or menstruation). This period is called "Proesterus" as it is the time that precedes estrus, when males are attracted to non-receptive females. Proestrus generally lasts for approximately nine days.

Next, is the real heat cycle, referred to as Estrus. This is the period of time when the moons align and the female is receptive. This is the true breeding period. Estrus lasts approximately five to nine days.

Estrus, together with proestrus in known as the time of being "in heat".

The tired phase is called diestrus. It is the period of time after the heat cycle. It lasts approximately 56 to 58 days in the pregnant bitch, and 60 to 100 days in the non-pregnant bitch.

Lastly, there is a time called "Anestrus" that is the period of reproductive quiescence. The bitch has no attraction to or from the male. Anestrus generally lasts four to five months.

A couple articles that might be helpful to you are The Heat Cycle of Dogs and The Stages of Canine Reproduction

Best of luck!

Dr. Debra

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